U.S. patent number 6,551,501 [Application Number 09/585,313] was granted by the patent office on 2003-04-22 for combined process for improved hydrotreating of diesel fuels.
This patent grant is currently assigned to Haldor Topsoe A/S. Invention is credited to Michael Brorson, Barry H. Cooper, Kim Gr.o slashed.n Knudsen, Darrell Duayne Whitehurst, Per Zeuthen.
United States Patent |
6,551,501 |
Whitehurst , et al. |
April 22, 2003 |
Combined process for improved hydrotreating of diesel fuels
Abstract
Described herein is a combined process for improved
hydrotreating of diesel fuels, in which the feed to be hydrotreated
is pretreated with a selective adsorbent prior to the hydrotreating
step to remove polar materials, especially nitrogen containing
compounds (N-compounds). The selective adsorption process can
employ either liquid or solid adsorbents. After contact of the
adsorbent with the diesel fuel feed, the adsorbent containing
undesired polar compounds is separated from the diesel fuel. The
separated adsorbent is then subjected to a two step procedure for
regeneration.
Inventors: |
Whitehurst; Darrell Duayne
(Titusville, NJ), Brorson; Michael (Charlottenlund,
DK), Knudsen; Kim Gr.o slashed.n (Virum,
DK), Zeuthen; Per (Birker.o slashed.d, DK),
Cooper; Barry H. (Charlottenlund, DK) |
Assignee: |
Haldor Topsoe A/S (Lyngby,
DK)
|
Family
ID: |
8097427 |
Appl.
No.: |
09/585,313 |
Filed: |
June 1, 2000 |
Foreign Application Priority Data
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|
|
|
Jun 2, 1999 [DK] |
|
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1999 00776 |
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Current U.S.
Class: |
208/211; 208/15;
208/254R |
Current CPC
Class: |
C10G
67/04 (20130101); C10G 25/003 (20130101); C10G
21/06 (20130101); C10G 67/06 (20130101); C10G
2300/201 (20130101); C10G 2300/1055 (20130101); C10G
2300/202 (20130101); C10G 2400/04 (20130101) |
Current International
Class: |
C10G
67/04 (20060101); C10G 67/00 (20060101); C10G
67/06 (20060101); C10G 045/00 (); C10L
001/04 () |
Field of
Search: |
;208/15,211,254R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Jean P. Teas, "Graphic Analysis of Resin Solubilities", vol. 40,
No. 516, Jan. 1968, pp. 19-25. .
D. Duane Whitehurst, et al. "Present State of the Art and Future
Challenges in the Hydrodesulfurization of Polyaromatic Sulfur
Compounds", Advances in Catalysis, vol. 42; pp. 345-471. .
Michael J. Girgis, et al. "Reactivities, Reaction Networks, and
Kinetics in High Pressure Catalytic Hydroprocessing", Ind. Eng.
Chem. Res., vol. 30, No. 9, 1991; pp. 2021-2058. .
P.B. Weisz, et al. "Superactive Crystalline Aluminosilicate
Hydrocarbon Catalsts", Journal of Catalysis 4 (1965); pp.
527-529..
|
Primary Examiner: Dang; Thuan D.
Attorney, Agent or Firm: Dickstein Shapiro Morin &
Oshinsky, LLP
Claims
What is claimed is:
1. A combined process for improved hydrotreating of diesel fuels,
which comprises the following steps: (a) contact of the fuel to be
hydrotreated with a selective solid adsorbent to remove inhibiting
compounds from the fuel, the adsorbent having an acid activity, as
measured by the standard hexane cracking test, --alpha test--,
which falls in the range of 0.3 to 10 alpha, the adsorbent
including an equilibrium FCC catalyst; (b) separation of the
adsorbent, containing the inhibitors, from the fuel with a reduced
inhibitor level without significant loss of the fuel; (c)
regeneration of the adsorbent and recycle of the regenerated
adsorbent back to the adsorption zone; and (d) hydrotreating the
fuel with a reduced inhibitor level to produce a clean diesel
fuel.
2. The process of claim 1, in which the adsorbent is selected from
the group consisting of a liquid or a solid.
3. The process of claim 1, in which the fuel being treated includes
a liquid phase.
4. The process of claim 1, in which the fuel being treated includes
a vapor phase.
5. A combined process for improved hydrotreating of diesel fuels,
which comprises the following steps: (a) contact of the fuel to be
hydrotreated with a selective adsorbent to remove inhibiting
compounds from the fuel; (b) separation of the adsorbent,
containing the inhibitors, from the fuel with a reduced inhibitor
level without significant loss of the fuel; (c) regeneration of the
adsorbent and recycle of the regenerated adsorbent back to the
adsorption zone; and (d) hydrotreating the fuel with a reduced
inhibitor level to produce a clean diesel fuel, wherein the
adsorbent includes a solid catalyst that is circulating within a
catalytic refinery process in close proximity to the process of
steps (a)-(d) and circulating solid catalyst is diverted to the
adsorption zone, and the solid catalyst, which adsorbs the
inhibitors, is separated from the treated fuel and is returned to
the catalytic refinery process at a point, where any remaining
treated fuel can be recovered, and the solid catalyst is then
passed on to the regeneration zone of the catalytic refinery
process.
6. The process of claim 5, in which the adsorbent is a solid, which
is basic in nature.
7. The process of claim 5, in which the adsorbent is a solid, which
is acidic in nature.
8. The process of claim 5, in which the acidic solid adsorbent has
an acid activity, as measured by the standard hexane cracking test,
--alpha test--, which falls in the range of 0.3 to 10 alpha.
9. The process of claim 5, in which the acidic solid adsorbent
includes an equilibrium FCC catalyst.
10. The process of claim 5, in which a sulphur content of the fuel
has been reduced from at least 500 ppm total sulphur to produce the
clean diesel fuel having a sulphur content of less than 500 ppm
total sulphur.
11. A combined process for improved hydrotreating of diesel fuels,
which comprises the following steps: (a) contact of the fuel to be
hydrotreated with a selective liquid adsorbent having solvent
parameters which fall within the desired area defined in FIG. 4, to
remove inhibiting compounds from the fuel; (b) separation of the
adsorbent, containing the inhibitors, from the fuel with a reduced
inhibitor level without significant loss of the fuel; (c)
regeneration of the adsorbent and recycle of the regenerated
adsorbent back to the adsorption zone; and (d) hydrotreating the
fuel with a reduced inhibitor level to produce a clean diesel
fuel.
12. The process of claim 11, in which a sulphur content of the fuel
has been reduced from at least 500 ppm total sulphur to produce the
clean diesel fuel having a sulphur content of less than 500 ppm
total sulphur.
Description
FIELD OF INVENTION
The present invention relates to hydrotreating of diesel fuels and
in particular to improvement of those processes in a staged
process.
BACKGROUND
The need to produce extremely clean transportation fuels is
continually increasing. Future standards are being set, which
cannot be achieved with existing process equipment. Although
improved commericial catalysts are available, they are not
sufficiently active to meet the increasingly more strict
requirements for high quality commercial fuels, and thus
modifications of process equipment are also necessary. Such changes
in process equipment will be expensive and there is a need to
identify novel processes to meet these requirements.
DETAILED DESCRIPTION
Overall Process Description
It is in the context of the above problems that the present
invention was conceived. When the sulphur level must be lowered to
less than 500 ppm sulphur, the conversions that are required
involve desulphurization of highly substituted dibenzothiophenes,
especially those in which the substituents are present on the
aromatic rings adjacent to the heterocyclic sulphur atom. We will
refer to such compounds as refractory sulphur compounds
(RS-compounds). A typical example of such a compound is
4,6-dimethyldibenzothiophene (46 DMDBT). We have found that the
conversion of the most refractory sulphur (RS) compounds (such as
46 DMDBT) in diesel fuels is made even more difficult by the
presence of certain other components found in normal feeds to
diesel hydrotreaters. Such compounds are referred to as inhibitors
for hydrodesulphurization (HDS).
We have discovered that if such inhibitors are selectively removed
from the feed and the feed containing less inhibitors is
hydrotreated under typical commercial conditions used in today's
refineries, then the RS-compounds can be readily removed by
hydrotreating using conventional catalyst loadings and process
conditions. The degree to which the inhibitors are removed will
depend on the particular adsorbent used and the cost of the removal
process. In many instances, it is not necessary to remove all of
the inhibitors to experience the benefits of our combined process.
For ease of discussion, we will refer to diesel fuels which have
been contacted with adsorbents for the inhibitors as "inhibitor
free" diesel fuels, however, we do not mean to imply that 100% of
the inhibitors have been removed. FIGS. 2 and 3 and Example 1
illustrate this point.
Hydrotreating Process
The hydrotreating step of the combined process scheme of this
invention, shown in FIG. 1, can be any conventional hydrotreating
process. This includes fixed or ebulated bed operations at
conventional operating conditions such as temperatures in the range
of 250.degree. C. to 450.degree. C., preferably 300.degree. C. to
380.degree. C. Pressures are also conventional such as 20-60 atm of
hydrogen, and preferably below 40 atm of hydrogen. Higher
temperatures and pressures will also provide the benefits of the
present invention, however, lower pressures and temperatures are
preferred to avoid yield losses of valuable diesel fuels and to
avoid the need for construction of new process equipment in order
to achieve extremely strict sulphur standards such as less than 300
ppm sulphur or even more strict sulphur standards of less than 50
ppm sulphur.
Catalysts used in the hydrotreating step are preferably those
employed conventionally, such as mixed cobalt and/or nickel and
molybdenum sulphides supported on alumina and mixed nickel and
tungsten sulphides supported on alumina or silica. The combined
process of this invention will also benefit newly developed
catalysts such as those containing ruthenium sulfide and catalysts
using novel supports such as silica-aluminas, carbons or other
materials. For details on the state of the art in conventional
hydrotreating processes, we refer to "Hydrotreating
Catalysis--Science and Technology", by H. Tops.o slashed.e, B.S.
Clausen and F. E. Massoth, Springer-Verlag Publishers, Heidelberg,
1996.
Inhibitor Removal Processes
It is possible to envision many ways of removing materials, which
inhibit the hydrotreating process, especially the
hydrodesulphurization of RS-compounds. However, the removal of
inhibitors should be done in a practical way if this principle is
to be realized commercially. The method used for inhibitor removal
should be highly selective for only the inhibitors and should not
remove the valuable components of the diesel fuel or other
non-inhibiting components of the diesel fuel. An alternative
process would be to selectively remove the RS-compounds as
described in U.S. Pat. No. 5,454,933. However, in that patent the
yield of diesel fuel was not specified, and in attempting to
duplicate this patent, we have observed that the adsorbent carbon,
though showing some selectivity for RS-compounds, has a high
capacity for all diesel fuel components. When one attempts to
recover the valuable diesel fuel components, the RS-compounds are
also released, as the strength of adsorption is not high. Thus, it
may be possible to concentrate the RS-compounds, but not remove
them specifically. There are many different classes of materials
that can inhibit the HDS of RS-compounds.
It is well known that certain basic compounds such as quinolines
and acridines inhibit HDS reactions (see H. Tops.o slashed.e, B. S.
Clausen and F. E. Massoth, "Hydrotreating Catalysis--Science and
Technology", Springer-Verlag publishers, Berlin 1996; M. J. Girgis
and B. C. Gates, Ind. Eng. Chem. Res., pp. 2021-2058, Vol. 30 No.
9, 1991; D. D. Whitehurst, T. Isoda and I. Mochida, Advances in
Catalysis, pp. 345-471, Vol. 42, 1998; and references therein).
However, any compound that will compete with RS-compounds for
adsorption on the catalytic site will inhibit the HDS of the
RS-compound. Thus, in addition to basic compounds, other strongly
adsorbing species in the diesel fuel that is to be hydrotreated
will lower the rate of removal of sulphur from the diesel fuel. We
have found that such inhibitors are all highly polar materials that
may be selectively removed from the hydrocarbons and RS-compounds
by various adsorbents. By polar compounds we mean classical basic
compounds such as were described above, including their
benzo-analogs. These may be identified in diesel fuels by titration
with strong acids in non-aqueous media. Other inhibitors include
acidic nitrogen species, such as carbazoles, indoles and their
benzo-analogs. Such acidic N-compounds can be identified by
titration with strong bases in non-aqueous media. Still other
inhibitors include amphoteric compounds such as hydroxyquinolines,
and still other neutral compounds containing more than one nitrogen
in an aromatic ring system or compounds which contain both oxygen
and nitrogen in the same molecule. Further, inhibitors need not
contain nitrogen, but may e.g. be composed of highly polar oxygen
containing species.
Thus, it is possible to devise adsorption processes, which will
selectively remove certain chemical classes of inhibitors or
selectively remove essentially all inhibitor molecules by virtue of
their polar nature. We have devised several different means to
achieve selective inhibitor removal from diesel fuels using either
their chemical properties or their polar properties. The particular
method that is preferred will depend on the particular situation
and the specific diesel fuel that is to be processed. However, the
most preferred general method for inhibitor removal is based on
their polar nature. The following text describes the various
methods we have devised for use in the combined process of this
invention.
Liquid Adsorbent Processes
In the present invention, our approach is to selectively remove the
inhibitors for RS-compound conversion and then selectively
desulphurize the inhibitor free feed in conventional HDS
operations. We have found that only certain adsorbents have the
selectivity desired.
Liquid adsorbents can be identified using their solvent parameters,
f.sub.d, f.sub.p and f.sub.h, as defined by Teas [see J. P. Teas,
"Graphic Analysis of Resin Solubilities", J. Paint Technology 19,
40 (1968)]. To define the useful range of solubility parameters, it
is customary to construct a triangular diagram and identify an area
within the diagram in which the desired results are obtained. This
effective area reflects the solubility characteristics of desirable
solvents in terms of their solvent parameters, f.sub.d, f.sub.p and
f.sub.h, which reflect the solvents' dispersive, hydrogen bonding
and polarity characteristics, respectively.
FIG. 4 shows the region of desired properties in the present
invention. Solvents that have solubility parameters that fall
within the desired range shown in FIG. 4 will be able to
selectively remove the inhibitors, while rejecting the valuable
diesel fuel components. In this example, dimethylformamide,
dimethylsulphoxide and methanol containing 25% water are shown to
fall within the desired area for our process.
In FIG. 5, examples of solvents that are not suitable for our
process are shown. In this case water alone is a poor solvent for
the inhibitors, while toluene and acetone are not selective for the
inhibitors as they are good solvents for diesel fuel and do not
form a separate phase.
A further example of how two non-useful solvents may be combined in
specific proportions to make a mixture, which has the correct
solvent properties, is shown in FIG. 6. In this example, n-propanol
is a borderline adsorbent as it is too strong a solvent for the
desired inhibitor free fuel and water is too poor a solvent for the
inhibitors. A mixture of the two falls within our desired range of
solvent parameters.
A further advantage of some mixtures is that some specific
combinations form azeotropes (constant boiling mixtures), which
have the desired solvent parameters. This is the case shown in FIG.
6, where the azeotrope of water and n-propanol consists of 71.8%
n-propanol and 28.2% water. This azeotrope boils at a lower
temperature than either component and would thus retain constant
composition in the distillation step used for solvent recovery.
Another important property of the solvent used to remove inhibitors
is the density of the liquid. To operate a successful separation
process, the density of the solvent should have a lower or higher
specific gravity than the diesel fuel being treated. The difference
between the specific gravity of the diesel fuel and the solvent
should be at least 0.02 specific gravity units, and preferably more
than this value.
To select a pure solvent or mixture, which has the correct
solubility parameters for use in our process, one only needs to
find the solvent parameters of the solvent or components of the
mixture (from the literature or by experimental determination) and
plot them on a triangular diagram similar to the one shown in FIG.
4. If the plot of the solubility parameters falls within the
desired area of FIG. 4 then material will be useful for the process
of this invention. If a mixed solvent is to be used, the mixed
components should constitute a single phase in order to effectively
extract the inhibitors from the diesel fuel.
To recover the solvent for reuse, distillation or, in some
instances, a simple flash process can separate the solvent from the
dissolved inhibitors. The isolated inhibitors may be disposed of by
burning or in some cases they may serve as sources of
chemicals.
The process used for removing inhibitors with a liquid adsorbent
can be any conventional process used for liquid-liquid extraction
such as columnar counter current flow, stirred tank, hydroclone,
etc. It may also be staged to increase the efficiency or it may be
a single contact process, depending on the degree of separation
desired. An illustration of this stage of our invention for
selectively removing inhibitors with liquid adsorbents is given in
FIG. 7. The schematic diagram illustrated in FIG. 7 represents a
columnar countercurrent flow process. This illustration is only one
example of a process that can be used to selectively remove the
inhibitors prior to hydrotreating, but should-suffice to instruct
anyone skilled in the art as to how to conduct such a process.
The range of conditions, which may be used in this extraction
process, is quite broad and will depend on the particular solvents
used and hydrotreating feeds that are being treated. Ambient
conditions are preferred, but in some cases the efficiency of
inhibitor removal or the density difference between the solvent and
the diesel fuel may be optimized by raising or lowering the
temperature. However, the temperature should not be higher than the
boiling point of either the diesel fuel or the extraction solvent,
and the temperature should not be lower than the freezing or pour
point of the diesel fuel or extraction solvent. For ease of
extraction solvent recovery, the boiling point of the extraction
solvent should be considerably different from the diesel fuel
boiling range, and preferably the solvent should have a boiling
point lower than the lowest boiling component of the diesel fuel,
or the lowest boiling inhibitor in the diesel fuel.
Solid Adsorbent Processes
Another version of the present invention is to use a solid
adsorbent in the inhibitor adsorption step. In this mode, many
process variations are possible. The adsorption process may be
conducted in a fixed bed operation or in moving beds, such as
fluidized beds, ebulated beds, or simple moving beds. FIGS. 8 and 9
illustrate two examples of such processes. For all cases in which
solid adsorbents are used, three integrated steps are needed for
the overall process. Firstly, the solid adsorbent is contacted with
the diesel fuel to remove inhibitors. Secondly, the solid is
separated from the physically adsorbed inhibitor free fuel.
Thirdly, the solid adsorbent, containing strongly held inhibitors
is regenerated to provide inhibitor free adsorbent, which is
reused.
In FIG. 8 two fixed beds are shown, in which one is in the
adsorption mode, while the other is in the regeneration mode. The
inhibitor free fuel is predominantly separated from the solid
adsorbent by merely passing the diesel fuel through the fixed bed
of adsorbent. However, a small amount of inhibitor free fuel is
retained on the adsorbent at the end of the adsorption cycle, and
this inhibitor free fuel is recovered prior to the regeneration
step. Inhibitor free recovery is achieved by a stripping operation
with a hot gas such as steam, hydrogen, refinery gaseous fuel, or
other refinery gases produced as byproducts from another refinery
process. The stripping operation can also be conducted with a light
liquid, such as a C4-C7 hydrocarbon, but this stripping liquid
should then be recovered with some stripping gas, prior to the
adsorbent regeneration.
In this mode of inhibitor adsorption, the diesel fuel constitutes a
liquid phase. The preferred temperature range for this mode of
operation is from ambient to slightly below the initial boiling
point of the diesel fuel being treated. This temperature range is
generally between 15.degree. C. to 300.degree. C., but could also
be conducted at sub-ambient temperatures if desired. The preferred
range is from 20.degree. C. to 200.degree. C.
The adsorption cycle length is determined by the capacity of the
adsorbent to remove the inhibitors from the diesel fuel feed. This
is generally determined by analysis of the inhibitor free fuel for
N-compound content. The preferred level of nitrogen in the treated
inhibitor free fuel is generally below 200 ppm, and, more
preferred, the level should be below 100 ppm, or even more
preferred less than 20 ppm. At this level of nitrogen in the
inhibitor free fuel, the subsequent hydrodesulphurization (HDS) is
quite facile, and levels of sulphur in the product of less than 20
ppm can be achieved under mild conventional process conditions
including lower pressures such as 30 atm of hydrogen as will be
shown in the examples.
In another embodiment of this invention, the adsorption step can be
conducted at elevated temperatures, where the diesel fuel is in the
vapor phase. This temperature should be high enough for the diesel
fuel to be in the vapor phase, but low enough for the cracking of
the valuable diesel fuel not to occur. The temperature should also
be low enough such that inhibitors are adsorbed by the solid
adsorbent and are not released back into the inhibitor free fuel
stream. In this mode of operation, the temperature range is
generally from 300.degree. C. to 450.degree. C., and the preferred
temperature range is from 350.degree. C. to 400.degree. C. When
operating in this mode, the inhibitor free fuel is not
substantially adsorbed by the solid adsorbent, and the stripping
operation may in some instances not be necessary. The regeneration
of the adsorbent is conducted as described above, when the
adsorbent's capacity for removing the inhibitors has been reached.
In this mode, the level of nitrogen in the effluent, inhibitor free
fuel, again determines the capacity of the adsorbent to remove
inhibitors. As described above, the level of nitrogen in the
effluent is preferably below 200 ppm and even more preferred below
20 ppm.
In the regeneration step, it is preferable to restore the solid
adsorbent's capacity, so that it may be recycled back to the
adsorption zone and reused. Such regeneration can be either
oxidative, i.e. by burning in a fixed bed operation, or reductive.
In some cases it may be desirable to heat exchange the regenerated
hot solid adsorbent, either directly or indirectly to recover the
heat from the combusted polar compounds and/or to cool the
adsorbent to the desired temperature for the adsorption zone. For
hydrogenative regeneration, the inhibitors adsorbed on the
adsorbent may be removed by high temperature contact with a gas
containing molecular hydrogen, such as pure hydrogen or a refinery
off gas containing a substantial portion of molecular hydrogen.
This contact with hydrogen can be done at atmospheric or elevated
pressures, but it is essential that the temperature be above
400.degree. C. These regeneration procedures should be conducted at
temperatures, which do not lower the surface area of the solid
adsorbent, but substantially remove all of the inhibitors as
gaseous products. The preferred temperature range for these
regeneration steps is from 400.degree. C. to 1000.degree. C., and
even more preferred, between 500.degree. C. to 700.degree. C. In
some instances, the solid adsorbent may contain catalytic
additives, which enhance the regeneration process. For example, in
oxidative regenerations, oxidation catalysts such as calcium,
magnesium, iron, potassium or sodium may be added, and in such
instances, the preferred combustion temperature is 350.degree. C.
to 500.degree. C. Hydrogenative regenerations may be enhanced by
hydrogenation catalysis, such as nickel, iron, platinum, palladium,
or other group VIII metals.
Other embodiments of this invention include inhibitor removal
steps, in which the solid adsorbent is continuously circulated
between the adsorption step in one vessel and the regeneration step
in a separate vessel. Such processes include moving beds, ebulated
beds, hydroclones, fluidized beds, etc. with external regeneration.
These moving bed processes can be stand-alone operations or can be
integrated with existing refinery equipment. In one preferred
embodiment of this invention, the inhibitor removal step is
integrated with an existing FCC operation in the refinery. In this
embodiment, the adsorbent comprises the steady state, or
equilibrium, FCC catalyst. FIG. 9 illustrates one example of this
type of integrated process. As can be seen in the figure, the
equilibrium catalyst is taken out as a side stream just after
regeneration and is then contacted with the diesel fuel feed that
contains inhibitors. The inhibitor free fuel is separated from the
FCC catalyst adsorbent and then hydrotreated to remove sulphur
contaminants as described above. The FCC adsorbent, containing
inhibitors and some physically adsorbed inhibitor free fuel, is
returned to the FCC operation in the stripper zone, where the
inhibitor free fuel is recovered as part of the FCC product stream,
and the inhibitors are retained by the FCC adsorbent. The FCC
adsorbent is admixed with FCC catalyst containing coke produced in
the FCC process and both are regenerated by combustion in the FCC
regenerator. In such an integrated process, the relative amounts of
equilibrium catalyst that are taken for the inhibitor adsorption
process and returned to the FCC cracking process are determined by
the content of inhibitors in the diesel fuel feed and the capacity
of the equilibrium catalyst to remove-those inhibitors.
As the regenerated FCC catalyst often exits the regenerator at
temperatures in excess of 900.degree. C., it is sometimes desirable
to cool the adsorbent FCC catalyst stream before the adsorption
step in order to avoid cracking of the diesel fuel. This can be
accomplished by either direct heat exchange with steam or refinery
gas or by indirect heat exchange with water which produces steam
for refinery heat or power generation. The degree of temperature
reduction will depend on which mode of operation is employed in the
adsorption step as described above.
Another embodiment of this invention is shown in FIG. 10, where the
adsorbent and fuel to be treated are contacted in a conical
circulating vessel, such as a hydroclone. Such types of vessels are
highly effective in separating solids and liquids at high
throughputs. In such a process, the critical features include
contact times between the solid and liquid sufficient to achieve
the desired level of inhibitor reduction, and flow velocities for
liquid and solid which can achieve separation of liquid and solid
without carryover of solid into the liquid exit stream. It is
within the scope of this invention to conduct such adsorption
processes at room temperature, at elevated temperatures or
sub-ambient temperatures, depending on the nature of the adsorbent,
the nature of the fuel that is being treated and the desired result
of the treatment. Anyone expert in this area can easily determine
the optimal conditions by experimental studies.
Suitable Solid Adsorbents
As will be shown in the examples, the choice of a suitable solid
adsorbent for inhibitors is the key to the success of this combined
process. We have found that many porous solids, when contacted with
diesel fuel feeds, can provide some benefit to the HDS of
refractory sulphur compounds (RS-compounds). However, the solid
adsorbents of choice should not only have the capability of
removing inhibitors, but they should be highly selective in this
removal and should have capacities for removing substantial amounts
of inhibitors before they are no longer effective. Once the
inhibitors have been adsorbed, the adsorbent should have the
properties that allow the recovery of physically adsorbed inhibitor
free fuel, while strongly retaining the adsorbed inhibitors. In
addition, the preferred solid adsorbents should have the durability
to withstand regeneration in a process in which the adsorbed
inhibitors are burned off of the adsorbent without losing their
effectiveness in multiple cycles of adsorption/regeneration.
It is possible to remove inhibitors using organic solid adsorbents,
and the use of such materials falls within the scope of this
invention. However, regeneration of such materials is more
complicated than for inorganic solids as combustion is not a viable
option. Suitable solids include porous carbons and intrinsically
porous ion-exchange resins (so-called macroreticular resins). As
will be shown in the examples, both strongly acidic and strongly
basic ion-exchange resins adsorb some inhibitors from diesel fuel
feeds, and such treatments of diesel fuel feeds allows a higher
degree of HDS of RS-compounds than is possible for untreated diesel
fuel feeds. However, regeneration of the ion-exchange resins, to
restore their original capacity for inhibitor removal, requires
large volumes of reagent liquids (e.g. aqueous or alcoholic acids
and bases) to remove the chemically adsorbed diesel fuel components
and restore the active sites within the ion-exchange resin. Carbon
adsorbents have similar disadvantages in that they are not highly
selective for only the inhibitors and they cannot be regenerated by
burning.
Another class of materials, which has been found to be effective
for the combined process of this invention, is porous strongly
basic alkaline earth oxide containing materials. Examples of such
materials include carefully calcined magnesium hydroxy carbonates
and porous Portland cements. These materials have the additional
advantage that they can function as oxidation catalysts, which
allows the use of lower temperatures in the regeneration step.
The most effective solids, which have been identified for this
application, are acidic silica/alumina containing materials having
surface areas greater than 100 m.sup.2 /g. Such materials include
pure silica/aluminas produced by co-precipitating silica and
alumina from a variety of precursors as well as composites
containing said silica/aluminas in combination with other
materials, such as zeolites. The acidity of these adsorbents can be
conveniently measured by the well-known "alpha" test as described
by Weisz and Miale, J. Catal. 4, 527 (1965). This test measures a
solid's ability to crack hexane at atmospheric pressure and
538.degree. C. Normal silica/aluminas containing about 4% aluminum
have alpha values of 1, whereas composites containing zeolites can
have alpha values exceeding 100. For the purposes of the present
invention, it is preferable to utilize solid adsorbents having
alpha values of from 0.5 to 10 and most preferred from 1-5. Such
materials are often used as catalyst supports or as composite
catalysts. They are highly durable and may be regenerated many
times without losing effectiveness in the application of the
present invention. This is especially true for FCC cracking
catalysts in which the binder or matrix (silica/alumina) comprises
about 60% of the composite and an acidic zeolite comprises the rest
of the composite. The acidity of such composites can be improved by
impregnation of or co-precipitation of the silica/alumina with
phosphorus containing acids prior to the final calcination step as
described in U.S. Pat. Nos 3,962,364, 4,044,065, 4,454,241 and
5,481,057. Such phosphorus treated silica/alumina containing
composites are also preferred materials in the present
invention.
EXAMPLES
Example 1
In order to evaluate the effect of removing inhibitors from diesel
fuels prior to the hydrotreating process, a series of experiments
were conducted, in which a standard diesel fuel was contacted in
various ways with several solid adsorbents, and the treated and
untreated feeds were subsequently desulphurized under standard
conditions. The composition of the diesel fuel feed is given in
Table 1.
TABLE 1 Composition of Standard Diesel Fuels ppm PPM % Aromatics
4MDBT 46DMDBT ppm N % H S.G. Mono Di Tri Total A 1.5990 330 160 293
12.3 0.8733 13.02 14.84 5.22 33.08 B 1.6050 291 142 327 0.8742
Diesel fuel B was percolated through a dry column of activated
chromatographic grade silica gel. In trial tests it was found that
all of the N-compounds, some of the S-compounds and some of the
aromatics were removed from the diesel fuel passing through the
silica gel column for the first two equivalent bed volumes of
diesel fuel, which were percolated. The next three equivalent bed
volumes of eluted diesel fuel contained essentially no N-compounds,
and the S-compounds and aromatics eluted at the same concentration
as in the parent feed. In the next four bed volumes of eluted
diesel fuel, it was observed that 54 ppm of N had eluted. Thus, it
took about two bed volumes of diesel fuel to come to equilibrium
with the silica gel column in terms of S-compounds and aromatics.
The capacity of this silica gel for selectively removing
N-compounds and leaving the S-compounds and aromatics in their
original concentration was about three bed volumes of diesel
eluting through the column after the column came to equilibrium
with the diesel fuel. Thus, it is important not to exceed the
capacity of the adsorbent for removing inhibitors from the diesel
fuel in the adsorbent step of this combined process.
Using a similar procedure, 16 liters of diesel fuel were prepared
in which the N-compounds and other polar inhibitors were removed
from the diesel fuel, but the S-compounds and aromatic hydrocarbons
were present in approximately their original concentrations. The
nitrogen content of the above treated "inhibitor free fuel" was
found to be about 7 ppm. This treated diesel fuel will be referred
to as inhibitor free diesel fuel 1C. Thus, the above treatment
removed over 97% of all of the N-containing inhibitors in the
diesel fuel. The aromatic hydrocarbons and sulphur level of this
inhibitor free fuel were found to be essentially the same as that
of the untreated diesel fuel, and the distribution and content of
RS-compounds was also the same as those of the untreated diesel
fuel. This "inhibitor free fuel" was then used for hydrotreating
studies to demonstrate how the reactivity of RS-compounds is
greatly improved by removing inhibitors in a pretreating step.
Example 2
The effectiveness of different liquid adsorbents for removing
inhibitors from diesel fuels were determined by contacting diesel
fuel A of Example 1 and various liquid adsorbents using a variety
of procedures as described in Table 2. The effectiveness was
evaluated by determining the amount of N-compounds removed from the
diesel fuel and the non-selective loss of diesel fuel to the
adsorbent liquid. As can be seen from the table, liquids like
acetone, and toluene are not effective as they completely dissolve
the diesel fuel, and there is no phase separation. Liquids such as
water give good phase separation, but do not extract the
inhibitors. Liquids, having just the right solvent parameters such
as dimethylformamide, selectively remove inhibitors, which gives a
high yield of treated diesel fuel. The table also shows that
azeotropic mixtures are effective adsorbents, but that some
azeotropes are more effective than others-e.g. i-propyl
alcohol/water azeotrope contains too little water, which results in
an excessive solubility of diesel fuel in the azeotropic mixture,
and gives a low yield of treated diesel fuel. By contrast, n-propyl
alcohol/water azeotrope contains the right amount of water, which
provides high selectivity for inhibitors with excellent yields of
treated diesel fuel product. Also shown in the table are
comparisons of conventional caustic extraction of the diesel fuel
in an attempt to selectively remove acidic inhibitors. This
extraction also produced an emulsion that was difficult to break.
The amount of material extracted was very little, and the level of
nitrogen in the treated fuel was not lowered significantly.
TABLE 2 Adsorption of Inhibitors by Liquid Adsorbents % of Oil
Nitrogen Content Lost to * Absorp- Liquid Extracted tion Adsorbent
Treatment Method Oil Extract Liquid A Dimethyl Formamide Single
Extraction 212 3881 4.0 B MeOH/H2O (25%) Three Extractions 135
20000 0.8 C MeOH/H2O (25%) PREP 4ext 3.5/1.5 237 D n-PrOH/H2O (28%)
Single Extraction 1.3 E i-PrOH/H2O (13%) Single Extraction 968 F
MeOH (trace H2O) Continuous L/L Extn 213 G i-PrOH/H2O (13%)
Continuous L/L Extn 23 H i-PrOH/H2O (28%) Continuous L/L Extn 3103
5.0 I Acetone Single Extraction (No Phase Separation) J Toluene
Single Extraction (No Phase Separation) K Water Single Extraction
>290 No Extract) Caustic Extractions I Aqueous 2N NaOH Single
Extraction 286 1522 0.1 J 75MeOH/25H2O NaOH Single Extraction 259
2512 0.9
Example 3
Adsorption of Inhibitors from Diesel Fuel A with Solid
Adsorbents.
To demonstrate the effectiveness of a variety of solid adsorbents
for removing inhibitors from diesel fuels before hydrotreating, the
diesel fuel A of Example 1 was contacted with selected solid
adsorbents at a ratio of 10 parts diesel fuel to 0.5 parts of solid
adsorbent. The original inhibitor contents of the diesel fuel were
estimated in three ways; total nitrogen content=293 ppm; the total
content of carbazoles=41.4 ppmN (estimated by GC/AED); and the
content of one specific inhibitor, 1-methylcarbazole (1 MCARB)=2.7
ppmN. These same indicators were measured after contact of the
diesel fuel with the solid at room temperature for 5-10 hr. It
should be noted that these treatments did not substantially affect
the concentration of RS-compounds or aromatic hydrocarbons in the
treated diesel fuel, but selectively removed the polar inhibitors.
The results summarized below in Table 3 show the following. Many
porous solid inorganic oxides remove inhibitors from the diesel
fuel. Both acidic adsorbents (C and D) and basic adsorbents (F, H,
J and K) are effective in removing inhibitors. To demonstrate the
need for high porosity in the adsorbent, examples E and F show that
a basic solid with no porosity, such as crystalline powdered
magnesium hydroxy carbonate, is not highly effective, but if it is
calcined at 450.degree. C. to decompose the carbonate and generate
porosity, an effective adsorbent can be produced. The Examples N, O
and P show that carbons are also effective adsorbents and further
that their effectiveness can be affected by pretreatment
conditions. It can be seen that Diahope (a commercially available
carbon) has superior adsorbent properties, if it is calcined in air
rather than in inert atmosphere. Microcrystalline basic silicates
and mixed oxides (Example J) as well as natural minerals (Examples
L and M) can also be used in this adsorption step.
TABLE 3 Effectivenes of Different Solid Adsorbents for Removing
Inhibitors % Inhibitor Removal Total SOLID ADSORBENTS Nitrogen
Carbazoles 1MCARB A Alumina 28.7 B Silica 36.9 C Silica/Alumina A
33.4 D Silica/Alumina B 27.3 E 4MgCO3Mg(OH)2.5H2O 5.8 F
4MgCO3Mg(OH)2.5H2O 40.4 52.4 59.1 Calc. 450.degree. C. G Ca(OH)2
5.7 22.7 H Zn(OH)2 6.3 16.0 I ZrO2 12.4 27.1 J Gray Cement (as rec)
17.8 34.3 K AMB-A27 71.8 82.8 L Florosil 12.3 M Talc 41.0 45.7 N
Diahope (450.degree. C./Air) 47.4 O Diahope (450.degree. C./N2)
27.6 P Carbosorb 9.1 24.8
Example 4
To demonstrate that the conditions used for preparing the adsorbent
prior to use in the adsorbent step are important and to show that
the ratio of adsorbent to diesel fuel is important, a series of
experiments were conducted in which adsorbents were prepared by
calcining magnesium hydroxy carbonate at different temperatures in
air for 2 hr and then contacting the adsorbent and diesel fuel in
different ratios at room temperature overnight. In all cases, 10
weight units of diesel fuel were treated with the weights of
adsorbents shown in Table 4. These results indicate that it is
important for the adsorbent to have a high surface area, and if the
level of inhibitors in the diesel fuel is to be lowered to less
than 100 ppmN, then surface areas of at least 100 m.sup.2 /gr are
required for this adsorbent. Other work indicates that for other
adsorbents, it is also important for the adsorbent to have at least
100 m.sup.2 /gr surface area. The data of Table 4 show also that
for any given adsorbent, there is a capacity limitation to its
ability to remove inhibitors from diesel fuel. For this specific
adsorbent, a ratio of 1 part adsorbent to 10 parts diesel fuel was
necessary to lower the nitrogen level of the treated diesel fuel to
less than 100 ppm N. Thus, for any adsorbent that is to be
considered for the combined process of the present invention, it is
necessary to establish the relative amounts of adsorbent used to
diesel fuel treated in order to achieve levels of inhibitors of
less than 200 ppmN in the treated diesel fuel. In subsequent
examples, we will show that the levels of inhibitors in treated
diesel fuels should be less than 200 ppmN for an effective process,
and that it is even more desirable to lower the level of inhibitors
in the treated diesel fuel to less than 100 ppmN. As is also shown
by the data of Table 4, the preparation method for the adsorbent is
critical for the specific adsorbent of this example. If the
temperature of preparation is too high, the surface area becomes
low, and the effectiveness of the adsorbent declines. This is
particularly important when one considers that the overall process
requires that the adsorbent be reused in a cyclic process. Thus, if
the adsorbent becomes saturated with inhibitor, it must be
regenerated and then used again for adsorption of inhibitors from
additional diesel fuel. If this regeneration is accomplished by
combustion, then the temperature must be controlled in such a way
that surface area is not lost during combustion of the adsorbed
inhibitors. Fortunately, in this specific example, the adsorbent
contains alkaline earth ions which catalyze combustion, and the
temperature necessary for complete removal of the inhibitors is
lowered to a range in which surface area is not lost during
regeneration.
TABLE 4 Importance of Surface Area and Diesel/Adsorbent Ratio
Surface Calcination Area Adsorbent Product Percent Temp. (C) m2/gr
weight ppm N Removed A none .about.1 0.5 276 5.8 B 450 149 0.5 170
40.4 C 450 149 1 92 67.7 D 450 149 2 49 82.8 E 550 88 1 182 36.1 F
550 88 2 119 58.2
Example 5
Use of Commercial Cracking Catalysts for Adsorption of
Inhibitors.
In some instances, it may be desired to integrate the adsorption
step of this combined process with another process in a refinery in
order to minimize the costs of equipment construction. Such
integrated processes can also take advantage of the availability of
very rugged inexpensive materials, which have been designed for
severe process applications, including processes in which the solid
experiences high temperature swings without loss of physical
integrity. One example of this was described in FIG. 9. In this
example, a small portion of the equilibrium catalyst circulating in
an FCC process is taken out as a side stream and used as the
adsorbent in the first stage of the combined process of the present
invention. The adsorbent, which becomes saturated with inhibitors,
is then recycled back to the stripper section of the FCC process,
where adsorbed inhibitor free diesel fuel is recovered, and the FCC
catalyst containing adsorbed inhibitors is then burned in the FCC
regenerator. Other examples of combined processes can include the
use of fixed bed hydrocracking processes, where the catalyst must
be periodically regenerated by combustion of coke on catalyst. Such
catalysts are also useful for the process of the present invention.
To demonstrate the ability of such commercial catalysts to perform
as adsorbents in the first stage of the combined process of the
present invention, several catalysts were contacted with the diesel
fuels of Example 1, and the amount of the inhibitors adsorbed by
these catalysts was determined. The results of these studies are
summarized here. A) A freshly prepared commercial FCC containing
40% rare earth Y-zeolite catalyst was contacted with diesel fuel A
in a ratio of 0.5/10 adsorbent to diesel fuel for 10 hr at room
temperature. The treated diesel fuel was then analyzed, and it was
found that the inhibitor level had been lowered by 8.5%. B) The
commercial FCC catalyst of Example 5A was used in an FCC cracking
process, and when the catalyst composition had reached steady state
(equilibrium catalyst), a sample was withdrawn and subsequently
used as an adsorbent for inhibitors in diesel fuel. This
equilibrium catalyst was contacted with diesel fuel A in a ratio of
0.5/10 adsorbent to diesel fuel for 10 hr at room temperature. The
treated diesel fuel was then analyzed, and it was found that the
inhibitor level had been lowered by 6.3%. Another portion of this
equilibrium FCC catalyst was contacted with diesel fuel at an
adsorbent to diesel fuel ratio of 2/10.
Analysis of this treated diesel fuel showed that the inhibitors had
been lowered by 31%. Similarly, another portion of this equilibrium
FCC catalyst when contacted with diesel fuel at an adsorbent to
diesel fuel ratio of 4/10 lowered the inhibitor level by 46%. C) A
commercial hydrocracking carrier containing 10% y-zeolite and 90%
alumina was used as an adsorbent for the inhibitors in diesel fuel.
The alpha value (hexane cracking activity at 500.degree. C.) of
this material was about 100. This material was contacted with
diesel fuel 1A in a ratio of 0.5/10 adsorbent to diesel fuel for 10
hr at room temperature. The treated diesel fuel was then analyzed
and it was found that the inhibitor level had been lowered by
27%.
Example 6
Preparation of Feeds for HDS of Diesel Fuels Containing Reduced
Inhibitor Levels.
In order to demonstrate the improvement in processability of diesel
fuels using the combined processes of the present invention, the
diesel fuels of Example 1 were treated with several adsorbents in
different ways to lower the inhibitor levels of the diesel fuels
prior to hydroprocessing. The adsorbents used in this first step of
our combined process and the resultant treated diesel fuels
containing a lower level of inhibitors consisted of the following:
a) Inhibitors removed by a liquid adsorbent in a liquid/liquid
extraction process; b) Inhibitors removed by an acid ion-exchange
resin in a batch contact process; c) Inhibitors removed by a base
ion-exchange resin in a chromatographic process; d) Inhibitors
removed by a porous basic inorganic solid in a batch contact
process; e) Inhibitors removed by an acidic catalytic cracking
catalyst in a batch contact process; f) Inhibitors removed by an
acidic hydrocracking catalyst in a batch contact process. A) The
diesel fuel of Example 1B was extracted 4 times with a 75/25
mixture of methanol and water at room temperature. The relative
volumes of diesel fuel to adsorbent were 2.3/1. Analysis of the
treated diesel fuel showed that this process removed 26% of the
inhibitors. B) The diesel fuel of Example 1B was contacted at room
temperature in a stirred vessel overnight with a strong acid
ion-exchange resin (Amberlyst-15 in protonic form). The volume of
diesel fuel treated was 3 volumes of diesel fuel per volume of
ion-exchange resin. The ion-exchange resin was removed by
filtration, and an analysis of the treated diesel fuel showed that
this process removed 39% of the inhibitors. C) The diesel fuel of
Example 1B was percolated at room temperature through a fixed bed
of a strong base ion-exchange resin (Amberlyst-A27 in the hydroxide
form), so that the total volume of diesel fuel treated was 2.4
volumes of diesel fuel per volume of ion-exchange resin. Analysis
of the treated diesel fuel showed that this process removed 76% of
the inhibitors. D) The diesel fuel of Example 1B was contacted at
room temperature overnight with a porous strong base inorganic
solid (calcined magnesium hydroxy carbonate). The volume of diesel
fuel treated was 10 parts by weight of diesel fuel per 1 part by
weight of the adsorbent. The solids were removed by filtration, and
the process was repeated a second time. Analysis of the treated
diesel fuel showed that this process removed 76% of the inhibitors.
E) The diesel fuel of Example 1B was contacted at room temperature
overnight with a commercial equilibrium FCC catalyst (containing
40% rare earth Y-zeolite). The volume of diesel fuel treated was
4.8 parts by weight of diesel fuel per 1 part by weight of the
adsorbent. The solids were removed by filtration. Analysis of the
treated diesel fuel showed that this process removed 39% of the
inhibitors. F) The diesel fuel of Example 1B was contacted at room
temperature over a weekend with a commercial silica alumina
cracking catalyst base. The volume of diesel fuel treated was 2.7
parts by weight of diesel fuel per 1 part by weight of the
adsorbent. The solids were removed by filtration. Analysis of the
treated diesel fuel showed that this process removed 94% of the
inhibitors.
Example 7
Hydrotreatment of Diesel Fuels Having Reduced Inhibitor
Contents.
The treated diesel fuels of Examples 1 and 6 as well as the parent
untreated diesel fuel of Example 1B were hydro-treated in a fixed
bed downflow reactor containing a commercial hydrotreating catalyst
composed of mixed nickel and molybdenum sulphides supported on
alumina. The feed compositions are summarized in Table 5. Several
reaction conditions were used and these are summarized together
with the results of the hydrotreating studies in Table 6. The
hydrogen to hydrocarbon ratios in all tests were 500/1 (N1/1).
These results show that in all cases, prior treatment of the diesel
fuel with a selective adsorbent results in dramatic improvements in
the subsequent hydrotreating process. This is particularly true for
the RS-compounds, where in all feeds (treated and untreated) the
initial level of RS-compounds were found to be 750-800 ppmS.
Thus, to reach a level of 100 or 50 ppmS in the final product, the
RS-compound conversions must be 87 and 93%, which is extremely
difficult to achieve without the use of the combined process of the
present invention.
The data also show that the total N level in the treated feed is
not an accurate indicator of the hydroprocess ability of the
adsorbent treated diesel fuel. To illustrate this, the adsorbent
treated feeds of Examples 7D, 7G and 7H all showed approximately
the same benefit in hydroprocess ability compared with the
untreated case (Example 7B), even though the adsorbent treatments
resulted in different levels of total nitrogen in the treated
products. These data show that adsorbents, which are acidic in
nature (for example 7D, 7H and 7I) are highly effective in removing
the strongest inhibitors in the diesel fuel. In addition, the data
show that if the level of total nitrogen is reduced to less than
100 ppmN and especially to a level of about 20 ppmN, the adsorbent
treated feed can easily be hydroprocessed to produce a product
which contains less than 50 ppms (Examples 7Q and 7R). Also shown
in the examples is the fact that with the combined process of the
present invention, it is possible to produce diesel fuels which
contain less than 10 ppm total nitrogen.
TABLE 5 FEED COMPOSITIONS Treatment ppmS ppm N Example 1A Untreated
15990 293.0 Example 1B Untreated 16050 327.0 Example 6A MeOH/H2O
16030 237.0 Example 6B AMB-15 15780 205.0 Example 6C AMB-A27 15870
80.0 Example 6D MgOx 16080 80.0 Example 6E FCC 15700 201.0 Example
6F HCB-130x 13970 21.0 Example 1C SiO2 14580 6.3
TABLE 6 HYDROTRATING CONDITIONS AND PRODUCT COMPOSITIONS % RS-
Temp. Pressure Product Composition Compound Example 7 Treatment
(C.) atm (H2) LHSV ppm S ppm N Removed A Untreated 328 30 1.64 1034
79.0 46.2 B Untreated 328 30 1.54 648 34.0 57.0 C MeOH/H2O 328 30
1.50 505 24.0 64.6 D AMB-15 328 30 1.55 290 11.0 72.1 E AMB-A27 328
30 1.51 412 11.0 67.8 F MgOx 328 30 1.69 350 6.7 70.0 G MgOx 328 30
1.51 303 6.0 74.0 H FCC 328 30 1.52 267 9.0 72.9 I HCB-130x 328 30
1.63 78 2.4 89.6 J SiO2 328 30 1.69 96 2.8 87.1 K Untreated 340 30
1.45 339 58.0 70.4 L MeOH/H2O 340 30 1.49 188 17.0 75.6 M AMB-15
340 30 1.51 113 7.4 84.9 N AMB-A27 340 30 1.53 173 8.0 76.8 O MgOx
340 30 1.47 117 4.4 84.3 P FCC 340 30 1.55 110 7.0 85.3 Q HCB-130x
340 30 1.43 41 2.6 94.5 R SiO2 340 30 1.47 46 2.5 93.8
Example 8
Demonstration of the Effect of Inhibitors on
Hydroprocess-ability.
To demonstrate that the treatments in Examples 1-7 truly
accomplished a selective removal of inhibitors from the diesel fuel
rather than causing some other change in the diesel fuel
composition, such as altering the sulphur compounds or aromatic
hydrocarbons in the fuel, a series of experiments were conducted,
in which specific N-compounds were added back to the inhibitor free
diesel fuel of Example 1C. The N-compounds, which were added back,
included 3-methylindole (3 MIND), 1,4-dimethylcarbazole (14 DMCB)
and acridine (ACRD), and each compound was added in such an amount
that the level of nitrogen in the inhibitor free diesel fuel was
increased by 300 ppmN. The untreated diesel fuel contained 327
ppmN. The three compounds used in this study represent three of the
major classes of N-compounds, which were identified in the diesel
fuel. Indoles and carbazoles are acidic and acridine is basic.
Thus, an acidic adsorbent should have a higher preference for
adsorbing basic compounds, such as acridine, while basic adsorbents
should have a higher preference for adsorbing acidic N-compounds,
such as indoles and carbazoles. Both acidic and basic N-compounds
are adsorbed by adsorbents having highly polar surfaces, and there
is a higher preference for adsorption of polyaromatic ring
N-compounds over single or double ring aromatic N-compounds. The
results of these studies are shown in Table 7. The results show
clearly that all three of the N-compound additives caused the level
of desulphurization of the diesel fuel to decrease and that the
basic additive, acridine, caused the greatest inhibition. The
lighter acidic additive (3-methylindole) caused the smallest
inhibition. Comparing these results with those of Example 7 shows
that adsorbents, which are selective for the removal of basic
N-compounds, will give the greatest benefit in the combined process
of the present invention. Such adsorbents are acidic in nature as
in Examples 7D, 7H and 7I.
TABLE 7 EFFECTS OF SPECIFIC INHIBITORS ON HYDROTREATING % RS- Temp.
Pressure Product Composition Compounds Example Treatment Additive
(C.) atm (H2) LHSV ppm S ppm N Removed A Untreated None 328 30 1.46
1034 79.0 46.2 B SiO2 None 328 30 1.47 93 2.1 87.5 C SiO2 3MIND 328
30 1.46 179 2.8 76.0 D SiO2 14DMCB 328 30 1.46 217 5.8 71.0 E SiO2
ACRD 328 30 1.46 1070 11.0 45.0
Example 9
For an adsorbent to be useful in our invention, it must perform
several functions. Firstly, it must selectively adsorb the
inhibitors from the oil; secondly, it must be regenerable without
causing any significant yield losses of any valuable oil that may
be physically adsorbed within the pores of the adsorbent; and
thirdly, the adsorbent must selectively retain the inhibitors
during the stripping step of the regeneration--prior to combustion
to restore the original adsorption capacity of the adsorbent. Thus,
some adsorbents may have good adsorption capacities for inhibitors,
but may not be able to retain the inhibitors during the stripping
step. Other adsorbents may have good inhibitor retention
properties, but may be too active and may induce cracking of
valuable oils during the stripping step. To illustrate such
problems, the following experiments were conducted. The diesel fuel
of Example 1B was treated with three different adsorbents (Examples
1C, 6E and 6F) to remove inhibitors from the diesel fuel. The
resultant adsorbents, containing both removed inhibitors and
physically adsorbed diesel fuel, were heated in the presence of a
stripping gas at elevated temperature to remove the adsorbed diesel
fuels, while selectively retaining the adsorbed inhibitors. In
these experiments, the ratio of diesel fuel to adsorbent was 10/1,
and the adsorbents containing both strongly adsorbed inhibitors and
physically adsorbed diesel fuel were isolated by filtration. The
stripping operation consisted of placing the recovered adsorbent,
containing the adsorbed inhibitors and diesel fuels, in a tubular
furnace and programming the furnace temperature from room
temperature to 450.degree. C., while flowing N.sub.2 gas through
the furnace. Diesel fuels, which were removed from the adsorbent,
were collected in a cooled trap, and any light cracked products
were allowed to escape. The yields of recovered treated diesel
fuels, compositions of the treated oils, yields of stripped diesel
fuels and the composition of stripped diesel fuels are summarized
in Table 8.
TABLE 8 Treatment of Diesel Fuel with Adsorbent and Adsorbent
Regeneration Oil recovered Oil adsorbed by filtration by solid
Diesel loss Calcd % of % of total % of total Oil recovered by due
to nitrogen amount amount stripping solid cracking; retained of oil
of oil % of % of in solid contacted contacted amount amount during
with with Calcd Calcd of adsorbed of adsorbed stripping Absorbent
solid % S ppm N solid % S ppm N oil % S ppm N oil step None 1.60
327 Silica 93 1.51 107 7 2.75 3140 100 2.04 2000 0 36 gel Equil 96
1.56 195 4 2.61 3670 100 2.05 1000 0 73 FCC HDC 94 1.54 53 6 2.50
4470 33 n.a. 2500 67 81 Base
It can be seen that all of the adsorbents are effective in
selectively removing inhibitors from the diesel fuel. The HDC base
has good retention of inhibitors in the stripping operation, but
induces excessive cracking of valuable diesel fuel during the
stripping step. By contrast, silica gel has low retention of
inhibitors in the stripping step but does not induce cracking. The
most preferred adsorbent is equilibrium FCC catalyst, which did not
induce cracking during the stripping step, while retaining the
inhibitors. The alpha values, as measured in the standard hexane
cracking test, of the three adsorbents were .about.0 for silica
gel, about 1 for the equilibrium FCC catalyst and about 100 for the
hydrocracking catalyst base (HCB-130x). Thus, it can be seen that
the most preferred adsorbents should have an intermediate alpha
activity of 0.3 to 10.
* * * * *